Various types of damper devices have been developed over the years to control the flow of fluid through ducts in HVAC systems. The damper devices are used to control the flow of air through the systems' air ducts and range from a simple hand-turnable damper vane often found in residential buildings to motor driven mechanical damper assemblies more commonly used in commercial and industrial structures. Another type of damper device employs an inflatable bladder or bellows to control fluid flow through a duct, and details of particularly useful bladder-type flow control devices and associated systems can be found in U.S. Pat. Nos. 4,545,524 and 4,702,412. One advantage of the bladder-type flow control devices shown in these patents is that they could be easily retrofitted into existing ducts with minimal difficulty.
Another prior art type of damper device is a mechanical damper assembly comprising a short piece of duct in which a damper vane is provided with a shaft that is pivotally mounted for rotation in the short piece of duct. The damper vane is rotated between open and closed positions by a motor mounted to and outside the duct piece and connected to the damper vane shaft.
The aforesaid type of mechanical damper assembly is somewhat difficult to install in an existing duct. Installation requires the duct piece of the damper assembly to be spliced into the existing duct. This involves cutting out a length of the existing duct and usually dismantling of the existing duct to enable such cutting and/or assembly of the duct piece between adjacent sections of the existing duct. This dismantling, cutting and reassembling of the ductwork is time consuming and therefore an expensive operation when performed by paid installers.
The damper vanes in prior art mechanical damper assemblies heretofore have been driven by both electric and fluid motors. A drawback of electric damper motors is that often their life cycle is comparatively short and limited, thereby making motor replacement a relatively frequent and expensive maintenance operation. Another problem is that, in systems employing a considerable number of electric motor driven dampers, relatively complicated wiring schemes and transformers are often involved, all adding to the cost and complexity of the overall system. Fluid motors eliminate the electrical wiring problems and often have comparatively longer life cycles, but they too have had drawbacks associated therewith. Even with so-called frictionless diaphragm-type fluid motors, the actuator rods thereof are engaged by bearings and wipers that still hinder free linear movement of the rods. Also, to reduce friction, the rods are made of hardened steel as opposed to less expensive materials.